Material application systems are used to apply one or more materials in one or more layers to an object. General examples are powder coating systems, as well as other particulate material application systems such as may be used in the food processing and chemical industries. These are but a few examples of a wide and numerous variety of systems used to apply particulate materials to an object and to which the present inventions can find realization and use.
The application of dry particulate material is especially challenging on a number of different levels. An example, but by no means a limitation on the use and application of the present inventions, is the application of powder coating material to objects using a powder spray gun. Because sprayed powder tends to expand into a cloud or diffused airborne spray pattern, known powder application systems use a spray booth for containment. Powder particles that do not adhere to the target object are generally referred to as powder overspray, and these particles tend to fall randomly within the booth and will alight on almost any exposed surface within the spray booth. Therefore, cleaning time and color change times are strongly related to the amount of surface area that is exposed to powder overspray.
In addition to exterior surface areas exposed to powder overspray, color change times and cleaning time are strongly related to the amount of interior surface area exposed to the flow of powder during an application process. Examples of such interior surface areas include all surface areas that form the powder flow path, from a supply of the powder all the way through the powder spray gun. The powder flow path typically includes a pump that is used to transfer powder from a powder supply to one or more spray guns. Hoses are commonly used to connect the supply, pumps and guns.
Interior surface areas of the powder flow path are typically cleaned by blowing a purge gas, such as pressurized air, through portions of the powder flow path. Wear items that have surfaces exposed to material impact, for example a spray nozzle in a typical powder spray gun, can be difficult to clean due to impact fusion of the powder on the wear surfaces.
Known supply apparatus for powder coating materials generally involve a container such as a box or hopper that holds a fresh supply of previously unused or ‘virgin’ powder. This powder is usually fluidized within the hopper, meaning that air is pumped into the powder to produce an almost liquid-like bed of powder. Fluidized powder is typically a rich mixture of material to air. Often, recovered powder overspray is returned to the supply via a feed hose and sieve arrangement. A venturi pump may be used to draw powder through a suction line or tube from the supply into a supply hose and then to push the powder under positive pressure through another hose to a spray gun. Such systems are difficult to clean for a color change operation because the venturi pumps cannot be reverse purged, the suction tubes and associated support frames and pumps retain powder, and there are exterior surfaces that need to be cleaned. The sieve is also challenging and time consuming to clean as it often is in a separate housing structure as part of the powder recovery system or is otherwise not easily accessible. Most of these components need to be cleaned by use of a high pressure air wand which an operator manually uses to blow powder residue back up into a cyclone or other powder recovery unit. Every minute that operators have to spend cleaning and purging the system for color change represents downtime for the system and inefficiency.
There are two generally known types of dry particulate material transfer processes, referred to herein as dilute phase and dense phase. Dilute phase systems utilize a substantial quantity of air to push material through one or more hoses from a supply to a spray applicator. A common pump design used in powder coating systems is the venturi pump which introduces a large volume of air at higher velocity into the powder flow. In order to achieve adequate powder flow rates (in pounds per minute or pounds per hour for example), the components that make up the flow path must be large enough to accommodate the flow with such a high air to material ratio (in other words lean flow) otherwise significant back pressure and other deleterious effects can occur.
Dense phase systems on the other hand are characterized by a high material to air ratio (in other words rich flow). A dense phase pump and related concepts are described in pending U.S. patent application Ser. Nos. 10/711,429 filed on Sep. 17, 2004 for DENSE PHASE PUMP FOR DRY PARTICULATE MATERIAL, and 11/140,759 filed on May 31, 2005 for PARTICULATE MATERIAL APPLICATOR AND PUMP, the entire disclosures of which are fully incorporated herein by reference, and which are owned by the assignee of the present inventions. This pump is realized in general by a pump chamber that is partially defined by a gas permeable member. Material, such as powder coating material as an example, is drawn into the chamber at one end by negative pressure and is pushed out of the chamber through the same end by positive air pressure. This pump design is very effective for transferring material, however, the present inventions are not limited to use with such a pump design. The present inventions are also not limited to use in powder coating material application systems, but rather may find use in any material handling system that needs to provide a supply of dry particulate material, including both dense and dilute phase systems.